Wide-band circulator

ABSTRACT

A wide-band circulator for micro-strip line, which utilizes a magnetic member, is described. A circular conductor having integral, radial extensions is disposed on one surface of said magnetic member, the ratio of the diameter of the magnetized region of said magnetic member to the diameter of said circular conductor being in the range between 1.4 : 1 to 2.1 : 1. The wide-band circulator does not need an impedance transformer as was necessary in the circulators of the prior art, so that it can be miniaturieed.

United States Patent [191 Miura et al.

[451 Aug. 14, 1973 WIDE-BAND CIRCULATOR Inventors: Taro Miura; Kiichi Nakamura;

Tadashi Hashimoto, all of Tokyo, Japan Assignee: TDK Electronic Company Ltd.,

Tokyo, Japan Filed: Aug. 5, 1970 Appl. No.: 61,272

Foreign Application Priority Data Sept. 13, 1969 Japan 44/72575 US. Cl. 333/L1, 333/84 M Int. Cl. 1101 5/12, HOlp 1/32 Field of Search 333/l.1, 84, 84 M,

References Cited UNITED STATES PATENTS 6/1969 Moose et al. 333 1Q1 3,513,413 5/1970 Nakahara et a1. 333/1.l 3,185,941 5/1965 Freiberg 3,277,399 10/1966 Simon 333/].1

Primary Examiner-Rudolph V. Rolinec Assistant Examiner-Marvin Nussbaum Attorney--C1ario Ceccon [5 7] ABSTRACT 7 Claims, 8 Drawing Figures 3 Shoots-Shoot l relative band mam m, I l

Patented Aug. 14, 1973 3 Sheets-Sheet :5

frequency (GHQ O 7 /w m 6 t g m 4 llllle I 1 O O 3 L M /2 w. 1 a H a 4 N L LJ- 3. 2 1 OII it 52 E2 @528 1 WIDE-BAND CIRCULATQR This invention relates to a wide-band circulator for micro-strip lines.

It is generally desired in a circulator to minimize the backward transmission energy and the insertion loss and to be utilized in a wide-band, but the frequency band width of conventional circulators is only to percent of the center frequency if the backwardtransmission energy is to be less than 20 dB (such a frequency band width is described as a 20 dB band, hereinafter). This is because in the circulators of the prior art the magnetic material is used as a kind of resonator which utilized the tensor susceptibility and hence its properties largely depended on frequency. Recently, in more advanced communication a wider frequency band has to be covered by a transmitter or a receiver, and at the same time a circulator of wider relative band width is demanded. If a single circulator having a wider band width is obtained, the variety of types of circulators can be reduced and the cost price of manufacture of the single wide-band circulator is reduced by mass production.

The object of this invention is to provide a miniaturized, wide-band circulator which meets the abovedescribed demands.

The circulator of this invention is characterized in that a circular conductor, having radially extended conductors integral with said circular section, is disposed on one surface of a magnetic member. The ratio 1 of the diameter of the magnetized region of said magnetic member to the diameter of said circular conduc tor being in the range of 1.4 l to 2.1 1.

This invention will be better understood from the following description with reference to the drawings, in which:

FIG. I is a plan view of a circulator of the prior art;

FIG. 2 is a plan view of another circulator of the prior art;

FIG. 3 is the characteristic curve of the circulator shown in FIG. 2:

FIG. 4 is a perspective view of one embodiment of the circulator of this invention;

FIG. 5 is a characteristic curve showing the relation between the relative band width and the ratio of the diameter of the magnetic member to that of the circular conductor;

, FIG. 6 is a plan view of one embodiment of the circulator according to this invention;

FIG. 7 is the characteristic curve of the circulator shown in FIG. 6; and

FIG. 8 is a characteristic curve showing the relation between the relative band width and the ratio of the diameter of the magnetized region of the magnetic memher to that of the circular conductor.

As shown in FIG. I, in the conventional circulator for micro-strip line, a magnetic member 3 is disposed on the ground plate 2 made of non-magnetic material. A circular conductor 4 is disposed on the magnetic member 3, and an impedance transformer 5 is connected between a connector 1 and the circular conductor 4.

The impedance transformer 5 is a M4 transformer (A being the wave length), using the magnetic member 3 as a dielectric material, for the purpose .of avoiding the reduction of the relative band width due to the frequency dependency ofthe impedance in the opening of the circulator. The magnetized region of the magnetic member 3 exists directly under the circular conductor 4 and extends therefrom about 20 percent of the diameter of said conductor because of the leakage of electro-magnetic wave out of the circular conductor.

It is assumed that the transmission mode of the microstrip is a simple TEM mode, and theoretical values derived from this assumption coincide with actually measured values. Using this assumption, the size of the circulator can be easily obtained by calculation. That is, the diameter D of the magnetic member 3 and the diameter d of the central circular conductor 4 are given by the following equations, where l is length of the impedance transformer 5:

f center frequency (MHz) ueff: effective magnetic permeability Eeff: effective dielectric constant If the magnetic member 3 of a circulator is made of YIG (yttrium-iron-garnet), 2 is 15, Eeff is 9 to 12 and hence the following relation is obtained from equations (1) to (3) under the assumption that ueff is 1:

An example of a conventional circulator for C-band, had these dimensions: D, d and D/d are 0.55 in., (14 mm), 0.24 in (6 mm) and 2.33, respectively, its center frequency f, is 6.6 GHz and relative b and width, Af/fl, is 0.33.

In another example of a conventional circulator whose magnetic member is generally triangle and l, w, D,d, and D/d are 0.14 in. (3.5 mm), 0.11 in. (2.6 mm), 0.51 in. (13 mm), 0.24 in. (6 mm) and 2.2, respectively, as shown in FIG. 2, the center frequency f,, is 7.4 GHz, relative band width Af/f, is 0.46 and insertion loss is 0.5 dB, as shown in FIG. 3.

According to this invention, a wide-band width and more miniaturized circulator can be obtained. As shown in FIGS. 4 and 6, a circular conductor 14 is disposed at the center of the upper surface of a magnetic disk 13 and microstrip are formed radially from the conductor 14, connectors being omitted for simplicity in these figures. The ratio D'ld of the diameter D of the magnetized region of the magnetic member 13 to the diameter d of the circular conductor 14 is set in a range between 1.4 and 2.1 If ferrite such as YIG (yttrium-iron-garnet) is used as the magnetic material of the circulator, the transmission mode of the microstrip line disposed thereon is not a simple TEM mode and it has been known that the band width of circulator depends mostly on the value of the ratio D'ld. The maximum relative b and width is obtained when Dld is about 1.9 as shown in Table l and FIG. 5. The measured values of Table 1 shows the variation of the relative band width Af/f when the diameter d of the central circular conductor 14 is constant 0.31 in. (8 mm); the whole magnetic member is magnetized and its diameter D is the variable. The width W of the microstrip is 0.055 in. or 0.079 in. (1.4 mm or 2.0 mm), the thickness of the magnetic member 13 is 0.059 in. (1.5 mm), f, is the lower limit frequency of the 20 dB band,f is the upper limit frequency of the 20 dB band, f is the center frequency, Afis equal to (f, f,), and the unit of frequencies is 0112.

TABLE 1 W D/d fl 1': fll).

(1.4 mm) 1.25 6.38 6.85 6.6 0.47 0.071 0.055 in. 1.50 5.95 6.38 6.2 0.43 0.069 1.63 5.85 6.50 6.2 0.65 0.105 1.75 5.40 6.66 6.0 1.26 0.210 1.88 4.65 7.90 6.3 3.25 0.520 2.00 5.66 7.46 6.6 1.80 0.270 2.13 6.10 7.10 6.6 1.00 0.150 2.50 6.61 6.90 6.8 0.29 0.043

(2.0mm) 1-25 6.26 6.72 6.5 0.46 0.071 0.079 in. 1.50 5.85 6.43 6.2 0.58 0.094 1.63 5.35 6.05 5.7 0.70 0.120 1.75 5.20 6.03 5.6 0.83 0.150 1.88 5.01 7.85 6.8 2.84 0.418 2.50 6.40 6.72 6.6 0.32 0.049

TABLE 2 .47 in. .25 in. .039 in. A,d=(12mm),d=(6.4 mm),r=(l.0mm)

W D/d f1 f: 1 f flfi (1.2 mm) 1.87 5.57 8.90 7.25 3.33 0.455 0.047 in.

.39 in. .19 in. .039 in. P1? if Qawtfli?m nlttitltqmml (1.0 mm) 2.08 8.32 11.00 9.56 2.68' 0.28 0.039 in.

Points A and B in FIG. show the property of circulators of references A and B in Table 2, respectively. The relation between the relative band width Af/f, and the ratio Dld is shown in FIG. 8, where D is 0.59 in. mm), d is 0.31 in. (8 mm), 1 is 0.059 in. (1.5 mm) and W is 0.055 in. (1.4 mm), and d is constant while the diameter D' of the magnetized region of the magnetic member 13 is varied. As is clear from FIG. 8, the relative band width Af/f, is in excess of 0.2 if the ratio Dld is more than 1.4. Although the word wide-band is not strictly defined, the relative band width of a usual circulator is about 0.1, and hence a circulator whose relative band width is more than 0.2 is generally called a wide-band circulator. Thus, as shown in FIG. 8, a wide-band circulator can be obtained if a circulator is designed so that DId is more than 1.4, because the relative band width Af/f, of a so-designed circulator exceeds 0.2. The relative band width is large when the width W of the microstrip on the magnetic member 13 is nearly equal to the thickness of the member 13, but as clear from FIG. 5, the ratio W/t less affects on the relative band width than the ratio D/d does. It is also shown in FIG. 5 that the upper limit of the ratio D/d is 2.1 for obtaining the relative band width Af/f, more than 0.2. Therefore, according to this invention, a wide-band circulator is provided when the following relation is established:

Where D is the diameter of the magnetic member 13 and d is the diameter of the central circular conductor 14. If only a part of the magnetic member 13 is magnetized, the diameter D in equation (5) is substituted by the diameter D of the magnetized region of the magnetic member. The condition of equation (5) is clearly different from that of equation (4) which describes the circulator of the prior art.

Thus, if the diameter D' of the magnetized region is in the range defined in equation (5), a wide-band circulator can be obtained regardless of the shape of the magnetic member.

FIG. 6 shows an embodiment of this invention wherein the diameter D of the magnetic member 13 is 0.59 in. (15 mm), the diameter d of the circular conductor 14 is 0.31 in. (8 mm), the width W of the micro strip is 0.055 in. (1.4 mm) and the ratio D/d is 1.87. FIG. 7 shows the properties of the circulator shown in FIG. 6;f is 4.6 G1-I z,f is 8.2 GHz,f, is 6.4 01-12, Afis 3.6 61-12, Af/f, is 0.56 and the insertion loss is 0.2 to 0.3 dB. As is clear from FIG. 7, the circulator of this invention has wider-band, smaller size and less insertion loss than the circulator of the prior art shown in FIG. 2.

The reasons whythe circulator of this invention has wide-band characteristics are as follows:

1. A magnetic field is applied on the microstrip and hence the characteristic impedance of the microstrip depends on frequency so that the frequency dependency of the circulator is compensated by that of the microstrip and the relative band width is increased.

2. The magnetic field extends far beyond the microstrip and the magnetized region covers the same area as said field so that the relative band width is increased.

If a part of the magnetic member 13, which part seems to have no relation with the microstrip and the circular conductor, is cut away to form triangle as shown in FIG. 2, the relative band width Af/f, is 0.44.

Thus, a circulator using a triangle magnetic member is inferior to a circulator using a circular one. This means, that the distance from the end of the circular conductor to the end of the magnetic member is reduced by cutting away a part of the magnetic member and hence the area affected by magnetization is also reduced so that the longer wavelength characteristic is affected more than the shorter wavelength characteristic, or f is increased.

According to this invention, a conventional impedance transformer whose length is shown in equation (2) is not necessary when a miniaturized wide-band circulator can be provided under the condition given by equation (5).

What is claimed is:

1. A wide-band microstrip circulator comprising a ground plate, a magnetic member placed on said ground plate, and a circular conductor having radial extensions therefrom and placed on said magnetic member, wherein the ratio of the diameter of the magnetized region of said magnetic member to the diameter of said circular conductor is in the range between 1.4: land 2.1:1.

2. A wide-band circulator as in claim 1 wherein said radial extensions are microstrip integrally connected to said conductor and wherein said extensions are within the magnetized region.

3. A wide-band circulator as in claim 1 wherein said magnetic member is circular.

4. A wide-band circulator as in claim 3 wherein the entire circular magnetic member is magnetized.

5. A wide-band circulator as in claim 2 wherein the ferrite material is yttrium-iron-garnet. 

1. A wide-band microstrip circulator comprising a ground plate, a magnetic member placed on said ground plate, and a circular conductor having radial extensions therefrom and placed on said magnetic member, wherein the ratio of the diameter of the magnetized region of said magnetic member to the diameter of said circular conductor is in the range between 1.4 : 1 and 2.1 :
 1. 2. A wide-band circulator as in claim 1 wherein said radial extensions are microstrip integrally connected to said conductor and wherein said extensions are within the magnetized region.
 3. A wide-band circulator as in claim 1 wherein said magnetic member is circular.
 4. A wide-band circulator as in claim 3 wherein the entire circular magnetic member is magnetized.
 5. A wide-band circulator as in claim 2 wherein the width of said microstrip is nearly equal to the thickness of said magnetic member.
 6. A wide-band circulator as in claim 1, wherein said magnetic member is of ferrite material.
 7. A wide-band circulator as in claim 6, wherein said ferrite material is yttrium-iron-garnet. 